1. Field of the Invention
The present invention relates to a pyrometallurgical smelting method of copper, and more particularly to an improvement of a method for charging the carbonaceous material into a flash smelting furnace which is utilized for the pyrometallurgical smelting of copper. Particularly, the present invention is an improvement of the method proposed in U.S. Pat. No. 5,662,730 in the name of Akagi et al.
In the smelting operation of copper, a portion of Fe in the charged materials is over-oxidized to form magnetite (Fe.sub.3 O.sub.4). This Fe.sub.3 O.sub.4 deposits on the bottom or side wall of the flash smelting furnace and acts as the protecting layer on the refractories of the furnace but, on the other hand, excess deposition of Fe.sub.3 O.sub.4 decreases the furnace's inner capacity. When the amount of Fe.sub.3 O.sub.4 so formed becomes such that excess coating may finally clog tap holes for the slag and matte, the tapping operation is made difficult. In addition, the slag and matte become difficult to separate from one another, and the viscosity of slag is so increased to increase the copper content of the slag.
2. Description of Related Arts
It is a known process in the flash smelting of copper to blow powder coke with or without finely particulated coal together with the copper-ore concentrate and heavy oil into a flash smelting furnace so as to decrease the copper loss in the slag and also to minimize fuel consumption (Japanese Unexamined Patent Publication No. 58-221,241).
It is a general pyrometallurgical-smelting practice of the flash smelting furnace that heavy oil, powder coke, finely particulated coal or the like are blown, as auxiliary fuel for heat compensation, together with the ore into the reaction shaft of the flash smelting furnace. The powder coke, finely particulated coal or the like is blown in U.S. Pat. No. 5,662,730 not only for the heat compensation but also for the reduction of Fe.sub.3 O.sub.4. Namely, a portion of the solid carbonaceous material added is not burnt in the reaction shaft but covers the melt in the reaction shaft's bottom, or alternatively the carbonaceous material is so finely particulated as to intrude into the melt in the reaction shaft's bottom.
In the copper flash-smelting practice with the addition of carbonaceous material, the air blast may be oxygen-enriched along with increase in the ore-feeding rate, or, alternatively, a high-S grade ore, S of which is the main fuel, is processed to prevent troubles in the furnace operation. In these cases, the thermal load applied to the flash smelting furnace, particularly the reaction shaft, becomes so increased that the amount of auxiliary fuel for heat compensation is decreased or becomes unnecessary. This indicates that, when a flash smelting furnace is operated under the conditions as described above, the amount of powder coke or particulated coal capable of addition into the reaction shaft is limited. This, in turn, means that the amount of carbonaceous material, which participates in the reduction of excess Fe.sub.3 O.sub.4, decreases, and the amount of Fe.sub.3 O.sub.4 in the slag accordingly increases. Various operational troubles described above are, therefore, incurred, and the copper loss in the slag increases.
In the pyrometallurgical smelting method proposed in U.S. Pat. No. 5,662,730, the carbonaceous material, whose grain size is under 100 .mu.m and is in a proportion of 65% or more, and whose grain size is from 44 to 100 .mu.m and is in a proportion of 25% or more, and which has 80% or more of fixed carbon content, is preliminarily mixed with the main charging material and is charged into a reaction shaft of a flash smelting furnace through an ore-concentrate burner. Alternatively the carbonaceous material is charged by means of a burner for exclusive use. In this method, although from 40 to 80% of the carbonaceous material is burnt in the reaction shaft, the unburnt coke has a small grain size, collides on and is captured by the molten particles of the copper-ore concentrate which simultaneously fall down through the reaction shaft. The captured carbonaceous material intrudes into the slag bath formed in the lower portion of the reaction shaft and then floats on the surface of the slag bath. Until the carbonaceous material floats onto the surface of the slag bath, the contact reduction of Fe.sub.3 O.sub.4 with the carbonaceous material occurs. By positively utilizing the contact reduction, the Fe.sub.3 O.sub.4 can be effectively reduced without incurring such troubles as excess reduction due to unburnt carbonaceous material, which floats and stagnates on the slag bath, and post-burning of unburnt carbonaceous material which scatters into a waste-heat boiler.
However, since the method proposed in U.S. Pat. No. 5,662,730 involves charging the carbonaceous material from the top of the reaction shaft, from 40 to 80% of the carbonaceous material is burnt in the reaction shaft and contributes to heat compensation as the auxiliary fuel. Therefore, when the amount of auxiliary fuel must be decreased along with increase in the feeding rate of the copper-ore concentrate, the amount of auxiliary fuel charged from the top of the reaction shaft must be accordingly decreased. As a consequence, the reduction amount of Fe.sub.3 O.sub.4 in the lower portion of the reaction shaft decreases, and the content of Fe.sub.3 O.sub.4 in the slag increases. Various troubles are, therefore, incurred.